ZBTB18 and microcephaly: Therefore, we suggest that: (1) AKT3 haploinsufficiency is sufficient to cause microcephaly with high but incomplete penetrance, (2) the heterozygous loss of ZBTB18 may cause microcephaly with a lower penetrance, and (3) other regions located more distally (including ZBTB18) may contribute to microcephaly in addition to AKT3 deletion.